Effects of spatial separation in visual pattern matching: evidence on the role of mental translation

Effects of the spatial separation between 2 simultaneously presented random patterns on the ability to determine whether the patterns are identical up to a translational displacement across the retina were investigated by using signal-detection methods. The patterns to be compared were presented on the periphery of an imaginary circle centered on fixation. Exposures were brief and postmasked. In Experiments 1 and 2, sensitivity (d') varied with exposure duration but not with the spatial separation between the patterns. In Experiment 3, the task was changed so that members of a "same" pair could differ by both a translation and a rotation. When the rotational component was O, d' was a monotonic decreasing function of the spatial separation between the stimuli. Apparently, in the special case, performance was based on mental alignment by a process of gradual mental translation of one of the members of a stimulus pair to the location of the other one.